Arc lamp electrode connection means



United States Patent O 3,532,922 ARC LAMP ELECTRODE CONNECTION MEANS Richard A. Huggins, Saratoga, Calif., assignor, by mesne assignments, to Varo, Inc., Garland, Tex., a corporation of Texas Filed June 9, 1969, Ser. No. 831,541 Int. Cl. H015 5/50 U.S. Cl. 313-331 12 Claims ABSTRACT F THE DISCLOSURE Electrical connection means for connecting the foot portion of an arc lamp electrode to an external contact comprising first and second ribbon conductor means one of which extends from an external lamp contact to one side of a tapered electrode foot and is then folded back upon itself so that the end thereof falls olf of the end of the electrode foot. The other ribbon is shorter than the rst and has one end positioned adjacent the rst conductor at a point intermediate its length and its other end extended into engagement with the other side of the electrode foot and then folded back upon itself to a point outside the electrode foot.

BACKGROUND OF THE INVENTION The present invention relates generally to arc lampy devices and, more particularly, to a novel manner of attaching electrical conductors to the electrodes of a short arc lamp.

One of the principal problem areas in the manufacture of short arc lamps is that involving the attachment of the electrodes to the external lamp contacts. Not only is it diflicult to form the necessary electrical contact to the tungsten electrodes because of the Welding problems involved when different metals are used for conductor and electrode, but consideration must also be given to the effect of the connection on the integrity of the lamp envelope which is usually heat shrunk thereabout.

When arc lamps of this type are utilized in environments -Where they are subjected to high shock and vibration, such as when used in rockets and missiles, for example, the lam-p structure is subjected to stresses which may cause it to become inoperable. One of these stresses is the tendency for the electrodes to be torn away from the electrical interconnect means as a result of the violent acceleration experienced in such environments. Thus, the choice of metals for use in forming the conductive path to the outside of the envelope must, in addition to being a good electrical conductor having reasonably high tensile strength, also be capable of forming a good electrical connection with the lamp electrode.

Another problem is the tendency of the lamp envelope to be damaged due to stress conditions set up in the envelope as the envelope is shrunk about the electrode during manufacture. This problem is particularly critical at the end of the foot portion of a tapered electrode since any sharp and abrupt termination of the metal in either the foot or the electrical connector can cause an undesirable stress condition to be created in the envelope. The high heat and diiferential expansion of the foot and envelope at this point can easily overburden any weakened section thereof.

Furthermore, if the envelope in shrinking over the connector should cause a partial or complete severance of the typically thin metal interconnect, the high currents passed through the device during operation may cause an explosive vaporization of the metal at the break which can itself shatter the envelope.

In accordance with certain prior art structure such as Mice are illustrated in the U.S. patent to Keller et. al. 3,256,459, electrodes have heretofore been connected to the envelope end terminals by a single ribbon-like conductor which is ywelded to a single side of the foot portion of the electrode. This, however, has for many applications been found unsuitable because of the tendency for the weld to be broken as the envelope shrinks over the tapered foot wedgedly forcing the electrode away from the conductor. This problem has been partially overcome by a novel modification made to the electrode foot which is disclosed in the copending U.S. application Ser. No. 813,429 led Apr. 4, 1969 in the name of Raymond E. Paquette and assigned to the assignee of the present invention.

OBJECTS OF THE INVENTION It is therefore, a principal object of the present invention to provide a novel electrical connection means the electrodes of an arc lamp so as to overcome the aforementioned disadvantages of the prior art apparatus.

Another object of the lpresent invention is to provide a novel means of attaching a conductive ribbon to an arc lamp electrode so as to produce a more reliable interconnection therebetween.

Still another object of the present invention is to provide a novel method of attaching an electrical conductor to the foot portion of an arc lamp electrode so as to provide redundant current paths with protective features which will not only tend to prevent conductor breakage but will minimize the effect of breakage should it occur.

SUMMARY OF THE PRESENT INVENTION In accordance with the present invention, a rst ribbonlike conductor is weldedly attached to one side of the tapered foot of an arc lamp electrode and a second shorter piece of ribbon conductor is attached to the other side of the electrode foot. The two conductors are then positioned side-by-side and are held in engagement by the envelope which is shrunk thereabout. The welded ends of the ribbons are folded back on each other so as to provide a cushioning means for preventing undue stress to be imposed on either the envelope of the conductor as the envelope is shrunk thereabout. A much more reliable lamp is thereby provided which can endure substanital shock and vibration without the consequent damage suffered by many prior art arc lamps of this type.

The advantages of the novel means of this invention 'yvill become apparent to those skilled in the art after having read the following detailed disclosure which makes reference to the several figures of the drawing.

IN THE DRAWING FIG. l is a partially broken away side elevation of an arc lamp having electrode connectors in accordance with the present invention.

FIG. 2 is an enlarged section of the electrical connection means of the present invention.

FIG. 3 is a top section of the electrical connection means illustrated in FIG. 2.

FIG. 4 is a top section of an electrical connection means illustrating an alternate welding intermediate in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. l of the drawing, there is shown a short arc bridge-Wire lamp 10 constructed in accordance with the present invention. The lamp 10 includes a lamp envelope 12 which is typically made of quartz and has mounted therein a pair of electrodes 14 and 16 which respectively form the anode and cathode of the device. The electrodes 14 and 16 are typically made of a refrac- 3 tory metal such as swaged tungsten and include respectively, main body portions 18 and 20, foot portions 22 and 24, and arc end portions 26 and 28.

The electrodes 14 and 16 may be identical in size, as is illustrated in the drawing, so that either electrode may be selected as the cathode, thereby making the lamp unpolarized. In the alternative, one of the electrodes may be constructed of a larger diameter than the other to form the hotter anode as is sometimes the practice in arc lamps. However, the fact that the lamp may be made nonpolarized is an advantage in that savings are made in the manufacturing cost and the user can connect the voltage supply to the lamp without regard to polarity. If the lamp is of a self-starting type, a bridge-wire 30y is typically connected across the electrode gap.

The foot portions 22 and 24 of the electrodes 14 and 16 respectively, are tapered to provide a means for supporting the electrode within the envelope and also to provide a means to which interconnect ribbons can be connected. The electrodes 14 and 16 are primarily supported in cantilever fashion Within the envelope 12 by shrinking the portions of the envelope 12 coextensive with the electrode feet.

In order to insure that the electrodes are fixedly secured against substantial axial movement within the envelope, the foot portions of the respective electrodes are provided with indentations 34 such as are described in detail in the aforementioned copending U.S. patent application by Raymond E. Paquette. Briefly, the foot portions are provided with indentations 32 which are wide enough to allow the softened quartz to flow thereinto as it is shrunk around the foot portions of the respective electrodes.

The conductive ribbons 34 and 36 are connected to the tapered electrode feet by welding and are typically made of molybdenum having a width of about Ma inch and a thickness of about 0.7 mil. The other ends of the ribbons 32 are similarly connected to terminal lugs 38 to which the external leads 40 may be attached. The other ends of the short ribbons 34 are positioned alongside the long ribbons 32 and are pressed into contact with each other by the envelope 12 as it is shrunk about them.

Referring now to FIGS. 2 and 3 of the drawing, the manner of attaching the ribbon conductors to the electrode will be discussed in detail. The electrodes are typically made of tungsten and the ribbons are typically made of molybdenum, and since molybdenum cannot be welded directly to tungsten, it has been found that the desired interconnection can be accomplished by placing small horseshoe-like sections 42 of tantalum wire in between the folded sections of the ribbons and the end of the electrode foot before the welding operation takes place. The tantalum pieces 42 then serve as an intermediate material, or bonding agent, between the two dissimilar metals and a suitable weld can be obtained therebetween.

Although the horseshoe-like or hairpin-like configuration serves as a convenient means for allowing the tantalum to be placed between the respective ribbons, it should be noted that other configurations of intermediate material can also be used. For example, a short section 44 of tantalum ribbon such as is illustrated in FIG. 4 can alternately be used to provide the desired weld. It is also to be understood that other types of metals can alternatively be used for any of the above described elements.

Returning now to FIG. 2 of the drawing, it will be seen that the ribbon 34 is welded to the tip 22 of the electrode 14 at a point short of its end and the ribbon is then folded at 44 and extended back along itself to terminate at a point 46 which is beyond the end of the foot 22. Likewise, the ribbon 36 is welded to the other side of the foot 22 at some intermediate point and is then folded at 48 and extended back along its length to terminate at the point 50. The other end 52 of the ribbon 36 is merely placed alongside the ribbon 34. It will be noted that all of the ribbon ends and ribbon folds are staggered with relation to each other so as not to provide an abrupt discontinuity in the thickness of the envelope 12 which could provide a stress line thereacross.

After the ribbons are weldedly connected to the electrodes the respective assemblies are extended into a tubular section of quartz material which is subsequently heated and vacuum shrunk at either end about the tapered foot portions 22 of the electrodes as illustrated. The ribbon folds and the space between the ribbons 34 and 36 at the end of the foot 22 provide a cushion-like effect for the quartz as it shrinks about the connection so that the likelihood of a damaging stress condition being set up in the quartz as it cools is substantially reduced. Furthermore, the resiliency of the folded ribbon acts together with the indentations 32 in the sides of the foot 22 to reduce the tendency of the quartz to dislodge the electrodes due to the squeezing effect of the quartz as it cools about the tapered foot portion.

Although the conductors illustrated in this disclosure have been depicted in the preferred embodiment as being ribbon-like in configuration, it is to be understood, of course, that they may comprise looped wires, braided ribbons or be of any other suitable configuration. The critical features are that the ends of the conductors be staggered and that a plurality of conductors be provided on either side of each foot portion so as to provide redundant current paths capable of supporting the operative current flow through the lamp should any of the ribbons become severed or otherwise rendered inoperative during the manufacturing, testing or operative stages of the device.

After having read the above disclosure, it is contemplated that any alterations and modifications of the invention will become apparent to those skilled in the art. It is therefore to be understood that this description is of preferred embodiments only which are disclosed for purposes of illustration and are in no manner intended to be limiting in any way. Accordingly, it is intended that the appended claims be interpreted as covering all modification which fall within the true spirit and scope of the invention.

What is claimed is:

1. In an are lamp including a sealed envelope and a pair of space apart electrodes having tapered foot portions, said electrodes being connected to conductor means which extend through the envelope foot enabling external electrical connection thereto, an improved conductor means comprising:

a rst elongated conductor means extending from an extremity of said envelope to one side of the tapered foot portion of said electrode; and

a second elongated conductor means of a shorter length than said first conductor means, said second conductor means having one end portion positioned adjacent an intermediate point of said first conductor means and the other end portion extending along the other side of said tapered foot portion of said electrode means, said first and second conductor means being welded to the respective sides of said foot lportion so as to provide a relatively smooth transition from electrode to conductor for the envelope which is shrunk thereabout.

2. In an arc lamp as recited in claim 1 wherein the end portion of said first conductor means extending along said one side of said foot portion is folded so as to extend back along itself to a first point beyond the tip of said tapered foot portion.

3. In an arc lamp as recited in claim 2 wherein said other end portion of said second conductor means which extends along said other side of said tapered foot portion is folded back upon itself and extends to a second point beyond the end of said tapered foot portion, said first and second points and said intermediate point being spaced fron;` each other.

4. In an arc lamp as recited in claim 3 wherein at 5 least one of said conductor means is of a ribbon-type material.

5. In an arc lamp as recited in claim `4 wherein said electrodes are made of a rst type of material and said conductor means are made of a second type of material and an intermediate means formed of a third type of material is positioned between said conductor means and said foot portion to act as a bonding agent for assuring a good bond therebetween.

6. In an arc lamp as recited in claim 5 wherein said intermediate means is of a Wirelike configuration suitably deformed to lie beneath said conductor means and provide a mechanically stable junction between said conductor means and said electrode.

7. In an arc lamp as recited in claim 5 wherein said intermediate means is an elongated strip suitably configured to lie beneath said conductor means so as to form a mechanically stable bond between said conductor means and said electrode.

8. A means for providing electrical connection to the foot portion of an electrode of an arc lamp device comprising:

a rst elongated conductor of a irst length extending from an end of the envelope of said arc lamp device to said electrode, one end of said rst conductor being extended along the foot portion of said electrode and weldably engaging said foot portion; and

a second conductor of a second length having one end positioned along said first conductor at a rst point intermediate the length thereof with the other end of said second conductor being extended along the other side of said foot portion and weldedly engaging said foot portion.

9. A means for providing electrical connection as recited in claim 8 wherein the end of one of said conductors at said electrode is folded back upon itself so as to extend beyond the tip of said electrode foot portion to a second point whereby a resilient cushion is provided between said electrode tip and said envelope when said envelope is shrunk thereabout.

10. A means for providing electrical connection as recited in claim 9 wherein the end of the other conductor at said electrode is likewise folded back upon itself so as to terminate at a third point off the end of said electrode tip.

11. A means for providing electrical connection as recited in claim 10 wherein at least one of said conductors has a ribbon-like configuration.

12. A means for providing electrical connection as recited in claim 11 wherein said conductors are of a irst type of material, said electrode is of a second type of material and an intermediate means of a third type of material is positioned between said conductors and said electrode so as to enable a good electromechanical bond to be formed between said conductors and said electrode.

References Cited UNITED STATES PATENTS 2,659,183 11/1953 Anderson 174-5064 XR DARRELL L. CLAY, Primary Examiner U.S. C1. X.R. 174-5064 

